Embodiments of the invention relate generally to synthetic jets and, more particularly, to arrays of micro-electromechanical (MEM) synthetic jets.
Synthetic jet actuators are a widely-used technology that generates a synthetic jet of fluid to influence the flow of that fluid over a surface. A typical synthetic jet actuator comprises a housing defining an internal chamber. An orifice is present in a wall of the housing. The actuator further includes a mechanism in or about the housing for periodically changing the volume within the internal chamber so that a series of fluid vortices are generated and projected in an external environment out from the orifice of the housing. Examples of volume changing mechanisms may include, for example, a piston positioned in the jet housing to move fluid in and out of the orifice during reciprocation of the piston or a flexible diaphragm as a wall of the housing. The flexible diaphragm is typically actuated by a piezoelectric actuator or other appropriate means.
Typically, a control system is used to create time-harmonic motion of the volume changing mechanism. As the mechanism decreases the chamber volume, fluid is ejected from the chamber through the orifice. As the fluid passes through the orifice, sharp edges of the orifice separate the flow to create vortex sheets that roll up into vortices. These vortices move away from the edges of the orifice under their own self-induced velocity. As the mechanism increases the chamber volume, ambient fluid is drawn into the chamber from large distances from the orifice. Since the vortices have already moved away from the edges of the orifice, they are not affected by the ambient fluid entering into the chamber. As the vortices travel away from the orifice, they synthesize a jet of fluid, i.e., a “synthetic jet.”
One major use for synthetic jets is in the cooling of heat-producing bodies, which is a concern in many different technologies. One such example is the use of synthetic jets in the cooling of integrated circuits in single- and multi-chip modules. A major challenge in the design and packaging of state-of-the-art integrated circuits in single- and multi-chip modules is the ever increasing demand for high power density heat dissipation. While current cooling techniques can dissipate about 4 W/cm2, the projected industrial cooling requirements in the coming years are expected to be 10 to 40 W/cm2 and higher. Furthermore, current cooling technologies for applications involving high heat flux densities are often complicated, bulky, and costly.
Traditionally, this need has been met by using forced convective cooling mechanisms, such as fans, which provide global overall cooling. However, what is often required is pinpoint cooling of a particular component or set of components rather than global cooling. Furthermore, magnetic-motor-based fans may generate electromagnetic interference, which can introduce noise into the system.
In applications where there is a heat-producing body in a bounded volume, issues arise with respect to cooling the body. Generally, cooling by natural convection is the only method available since forced convection would require some net mass injection into the system, and subsequent collection of this mass. The only means of assistance would be some mechanical fan wholly internal to the volume. However, often this requires large moving parts in order to have any success in cooling the heated body. These large moving parts naturally require high power inputs and are not practically implemented. Conversely, simply allowing natural convective cooling to carry heat from the body producing it into the fluid of the volume and depending on the housing walls to absorb the heat and emit it outside the volume, is also an inadequate means of cooling.
Accordingly, there is a need for a system and method for providing cooling of integrated circuits in single- and multi-chip modules. There is a further need for such a system to be small and provide effective cooling via convection so as to be useable in a bounded volume.